Magnetotransport through a pair of parallel ballistic conducting channels separated by an antidot is studied theoretically using models with magnetic edge states linked by unitary scattering matrices. Analytic solutions of the models are presented. A model is identified that exhibits abrupt phase shifts of magnetoconductance oscillations and beatlike conductance features similar to those that have recently been observed experimentally. The effect of temperature on the beatlike structures is discussed. Another possible explanation for the experimentally observed phase shifts is also mentioned.

We study the two-probe transport in a long narrow channel of two-dimensional electron liquid (a quantum wire) in a strong magnetic field normal to the plane. The wire is split into alternating parallel strips of compressible and incompressible liquids. When the temperature is not too low, in every transverse cross section of the wire the electrochemical potential is different in different compressible strips but is uniform within each strip. The equilibration rate between two neighboring compressible strips falls off exponentially with the distance between them (the width of the separating incompressible strip). Assuming a parabolic confinement potential and small disorder potential, we find the magnetic-field dependence of the strip widths. Using only this dependence, we calculate the shape of the magnetoresistance peaks. We show that the low-field sides of these peaks are much steeper than the high-field sides, in agreement with recent experimental data.

Intrasubband scattering rates are calculated for electrons and holes at finite temperatures in highly excited semiconductor strained-layer quantum-well structures. Carrier-carrier and carrier-phonon interactions are taken into account on an equal basis within the fully dynamic random-phase approximation for multisubband structures. It will be shown that the strain-induced changes in the valence-band structure exert a significant influence on the scattering rates of the electrons as well as the holes. The screening of carrier-phonon interaction by the electron-hole plasma in the coupled electron-hole-phonon system is discussed and analyzed.

Using numerical exact diagonalization and analytical variational calculations, we examine the effect of an electronic two-band structure on the persistent current of an interacting disordered one-dimensional ring. Several different features in comparison to a single band model are encountered. Among them are a transition in the magnitude of current for a critical ratio of the hopping elements in the two bands, and a large increase in the rms value of the persistent current for certain values of interaction and disorder. Possible experimental implications are discussed.

Raman scattering of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As epitaxial layers on InP and GaAs substrates have been investigated with a wide range of composition. It is found that the asymmetric broadening of LO phonon modes varies with composition as well as substrate. With the spatial correlation model, the Raman line shapes of the GaAs-like mode in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As epitaxial layers have been analyzed. It is found that the one-parameter spatial correlation model cannot explain the experimental results. According to the measurements of double-crystal x-ray diffraction (DXRD), we find strong correlation between the full width at half maximum of DXRD measurements and the line shapes of the Raman spectra. Thus, it is suggested that the Raman line shapes depend not only on the alloy disorder but also on the degree of structural dislocation in the heteroepitaxial system. Structural dislocation will change the intrinsic linewidth of the Raman spectrum which introduces an additional fitting parameter in the spatial-correlation model. Thus, our results provide a framework for the use of the two-parameter spatial-correlation model in the study of the compositional dependence of the Raman spectra in epilayer structures.

Excitations of the two-dimensional electron gas, including many-body effects, are calculated with a variational Monte Carlo method. Correlated sampling is introduced to calculate small energy differences between different excitations. The usual pair-product (Slater-Jastrow) trial wave function is found to lack certain correlations entirely so that backflow correlation is crucial. From the excitation energies calculated here, we determine Fermi-liquid parameters and related physical quantities such as the effective mass and the Landé g factor of the system. Our results for the effective mass are compared with previous analytic calculations.

Raman-scattering studies are reported for a vibrational mode with an eigenvector localized at planes of interface atoms of heterojunctions. These planar vibrational modes (PVM’s) are studied in a variety of structures formed in the III-V 6.1-Å semiconductor materials family of GaSb, InAs, and AlSb with interface planes involving GaAs or AlAs bonds. The results of these measurements are compared with calculations of the eigenvectors and eigenenergies of the PVM’s and are related to a simple one-dimensional model that describes the segregation of atoms during growth.

Two reconstruction structures are proposed for Bi adsorption on Si(100) based on a first-principles local-density-functional molecular-cluster study employing total energies and atomic forces. Bi dimers, rather than monomers, are predicted to form the basic structure on the Si(100) surface. At high coverage, Bi adsorption leads to the breaking of Si dimers, which in turn removes the reconstruction of Si(100)2×1. Our results appear to explain recent results of scanning tunneling microscopy experiments.

Negative differential conductivity is a well-known effect in semiconductor superlattices if a voltage is applied perpendicular to the layer structure. For highly doped superlattices, the appearance of electric-field domains has been found experimentally [H. T. Grahn et al., Phys. Rev. Lett. 67, 1618 (1991)]. In this paper we present a theoretical model which can explain these effects quantitatively. The model considers the lowest two subbands of the single quantum wells and includes resonant tunneling between adjacent wells, miniband conduction, and intersubband relaxation within each well. We obtain multistability of the current-voltage characteristic and various hysteretic transitions which arise upon sweeping the applied voltage, and which are associated with changes in the domain size.

In this paper, we calculate the first-order correction to the electron–longitudinal-optical- (LO)-phonon scattering in quantum wells due to dynamical screening at finite temperature. A many-body perturbative formalism is used to calculate the electron self-energy and electron-phonon scattering rate. Numerically solvable expressions for the polaron scattering rate are derived. When the electron wave vector (or plasma frequency) is much larger than the phonon wave vector, it is shown that the dynamic screening is reduced to static random-phase-approximation screening.

Unequal quantum-well capture rates of electrons and holes give rise to the accumulation of space charge which accelerates the capture of electrons and retards the capture of holes. This case is analyzed for the GaAs/${\mathrm{Ga}}_{0.7}$${\mathrm{In}}_{0.3}$As single-quantum-well system using two optical-phonon spectra: (a) bulk spectrum in both barrier and well, and (b) bulk spectrum in the barrier, confined hybrids in the well. Phonon confinement reduces the capture rate significantly. Equilibrated resonant capture times for a 50-Å well obtained are for bulk modes and for bulk and/or confined modes.

Surface electronic states of the Si(111)3×1-K surface are studied by means of angle-resolved ultraviolet photoelectron spectroscopy along the [112¯] and the [101¯] directions. It is found that the ${\mathrm{S}}_1$ state (∼0.2 eV below the Fermi level) of the 7×7 surface disappears and surface states ${\mathrm{S}}_2^{\prime }$ and ${\mathrm{S}}_3^{\prime }$ appear near the binding energy of ∼0.9 and ∼1.8 eV below the Fermi level in the spectra of the Si(111)(3×1)-K surface. Hence, the Si(111)3×1-K surface is no longer metallic like the Si(111)7×7 clean surface but is semiconducting. The saturation coverage of K on the Si(111)3×1-K surface is estimated to be 13 ML from comparison of the Si LVV Auger spectrum and the K 2p x-ray-photoemission-spectroscopy peak intensity ratio to that of the Si(111)δ7×7-K surface. From these results, we suggest a surface geometrical structural model for the Si(111)3×1-K surface.

Electron–acoustic-phonon scattering in a rectangular quantum wire is studied. The Hamiltonian describing the deformation-potential interaction of confined acoustic phonons with carriers is derived by quantizing the appropriate, experimentally verified approximate compressional acoustic-phonon modes in a free-standing rectangular quantum wire. The scattering rate due to the deformation-potential interaction is obtained for GaAs quantum wires with a range of cross-sectional dimensions. The results demonstrate that a proper treatment of confined acoustic phonons may be essential to correctly model electron scattering rates at low energies in nanoscale structures.

The effect of localized electron states on the photovoltage at a free semiconductor surface is analyzed. The analysis shows that surface-photovoltage spectroscopy (SPS) is inherently more sensitive to surface states than to bulk states. Moreover, a fundamental difference between the effect of surface and bulk states on the surface photovoltage (SPV) is shown. The analysis demonstrates that the same illumination-induced variation of the population at a surface and a bulk state may result in a significantly different dependence of the SPV on the illumination intensity. Under certain conditions, this difference makes it possible to distinguish between surface and bulk states by means of SPS. Analytical expressions for these relations are obtained under the depletion approximation, and are compared with the results of a numerical simulation. Experimental results obtained from InP samples demonstrate an application of the theory to practical distinction between surface and bulk states.

We present a rigorous analysis of the effects of electric fields on time-resolved photoluminescence spectra in semiconductors. It is based on the solution of the semiconductor transport equations using the drift-diffusion approxmation. The results show that the effect of the field alone on the photoluminescence decay can be distinguished from that of charge separation and field-enhanced surface recombination. The analysis is applied to two different sets of experiments. In the first, we use femtosecond luminescence upconversion to observe the ultrafast charge separation in the space-charge region, and screening of the electric field under high-injection conditions. The second group of experiments was conducted on heterostructures of GaAs/${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$P under externally applied bias using time-correlated single-photon counting detection in the picosecond time domain. The use of the method for extracting charge-transfer velocities across semiconductor interfaces is discussed.

The basic analytical properties of the linear differential operator describing the long-wave phenomenological model of polar optical modes in semiconductor nanostructures are studied under very general conditions. While full account is taken of the coupling between longitudinal and transverse parts of the mechanical vibration amplitude u and of u with the electrostatic potential field φ, the analysis holds for interfaces of arbitrary geometry and for any type of nanostructure. The Hermiticity of the linear differential operator, the orthogonality of the eigenvectors u, and the consequent completeness relation are established (i) without need to resort to the explicit form of the eigenvectors (ii) in a way which bears out the role of the matching rules at the interfaces. From this the amplitude of φ and the consequent electron-phonon interaction Hamiltonian are obtained for arbitrary geometry and structure under general conditions.

A quantitative study of the compressibility of the two-dimensional electron gas in GaAs heterostrutures is reported. Using a recently developed capacitive technique that avoids the large offset signals characteristic of conventional methods, high-precision compressibility data at both zero and high magnetic field has been obtained. The curious negative sign of the compressibility in certain regimes is shown to be a consequence of electron-electron interactions. Detailed numerical calculations show that the zero-field data are fully consistent with the known exchange energy, provided the finite thickness of the electron gas is properly included. At high magnetic fields, in the extreme quantum limit, the integrated compressibility signal is used to obtain a quantitative measure of the chemical potential discontinuity associated with the ν=1/3 fractional quantum Hall effect. Comparison with a theoretical model which includes quasiparticle interactions has allowed a determination of the inhomogeneous broadening due to density fluctuations and has provided evidence of a second, apparently distinct, source of disorder. While the origin of this disorder is not fully understood, the data are consistent with simple lifetime broadening of the quasiparticle states.

We use diffusion quantum Monte Carlo (DQMC) techniques to obtain accurate estimates of the components of the Kohn-Sham effective potential of density-functional theory for a model semiconductor, and the corresponding components of the energy functional, by determining the local potential which, when filled with noninteracting electrons, reproduces the DQMC electron density. The results are compared with the widely used local-density approximation. There is a large deviation in the exchange-correlation potential, a slight deviation in the electron density, but a very small deviation in the total energy and its components. We also use DQMC techniques to calculate the quasiparticle band gap, and hence the discontinuity Δ in the exchange-correlation potential on the addition of an electron.

Acoustic-phonon Raman spectra of GaAs/AlAs superlattices show two characteristic features. Sharp lines originate in crystal-momentum conserving backscattering by folded superlattice phonons. A continuous emission background with superimposed peaks and dips is observed due to disorder-induced scattering from modes of the whole folded acoustic-phonon dispersion. In this case, neither the crystal-momentum component ${\mathit{q}}_{\mathit{z}}$ along ${\mathit{q}}_{\mathrm{\parallel }}$ nor perpendicular to the growth direction is conserved. Even in high-quality samples the amount of disorder is such that both effects appear at the same time. These phenomena allow us to obtain information on growth-related and intrinsic parameters of semiconductor superlattices and multiple quantum wells. Gaps of the folded-phonon dispersion cause intensity anomalies in the background emission. From the ratio of such features at mini-Brillouin-zone boundary gaps, for which only ${\mathit{q}}_{\mathit{z}}$ is not conserved, to those at internal gaps, where both ${\mathit{q}}_{\mathit{z}}$ and ${\mathit{q}}_{\mathrm{\parallel }}$ can take arbitrary values, the degree of interface roughness and the lateral extent of growth islands are deduced. The resonance behavior of the continuous emission and relative changes of wave-vector conserving folded-phonon to background scattering intensities are analyzed in terms of homogeneous and inhomogeneous broadenings of interband critical points. Changes of the homogeneous linewidth with energy and temperature, as well as electron-phonon interaction constants, are determined.

Using a well-known singular gauge transformation, certain fractional quantized Hall states can be modeled as integer quantized Hall states of transformed fermions interacting with a Chern-Simons field. In previous work we have calculated the electromagnetic response function of these states at arbitrary frequency and wave vector by using the random-phase approximation in combination with a Landau-Fermi-liquid approach. We now adopt these calculations to a spherical geometry in order to facilitate comparison with exact diagonalizations performed on finite-size systems.